Ice making machine and ice cube evaporator

ABSTRACT

An evaporator includes a refrigerant conduit; and front and rear plates sandwiching the refrigerant conduit, each of the front and rear plates including: a plurality of ice forming columns; a set of first protrusions and a set of second protrusions defined therein, each first protrusion on the front plate and a corresponding first protrusion on the rear plate defining a respective active cavity and each second protrusion on the front plate and a corresponding second protrusion on the rear plate defining a respective passive cavity, the refrigerant conduit extending through each of the active cavities but not any of the passive cavities; and inner flat portions of the front plate and the rear plate facing each other to define respective spaced portions, wherein the active cavities and passive cavities are interspersed and separated by respective inner flat portions so as to define a plurality of ice forming sites.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/353,833 filed Nov. 17, 2016, which is a continuation-in-part of U.S.application Ser. No. 14/022,887 filed Sep. 10, 2013, which issued intoU.S. Pat. No. 10,107,538 on Oct. 23, 2018, which itself claims thebenefit of U.S. Provisional Application No. 61/699,171, filed Sep. 10,2012. The disclosures of these applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to an evaporator, an ice making machineincorporating the evaporator, and a process for making the evaporator.

Automatic ice making machines are well known and are typically found infood and drink service establishments, hotels, motels, sports arenas,and various other places where large quantities of ice are needed on acontinuous basis. Some automatic ice making machines produce flaked icewhile others produce ice shaped in a variety of configurations, whichare commonly referred to as cubes or nuggets.

Automatic ice making machines generally include a refrigeration systemhaving a compressor, a condenser, an evaporator, and an expansion valve.A series of individual ice forming sites are formed on the evaporatorand water is supplied to those sites by a water supply system by, forexample, trickling or spraying water onto the ice forming site. Therun-off of the water is usually recirculated within the water supply.The trickling or spraying methods of supplying water are normallypreferred because the methods produce clear ice while the static filledpockets method generally produces white or opaque ice.

Automatic ice making machines are normally controlled as a function ofthe amount of ice in an ice bin of the ice making machine. When thesupply of ice in the ice bin is insufficient, automatic controls cyclethe ice making machine through ice production and ice harvest tosupplement the supply of ice in the storage portion. In the iceproduction mode, the refrigeration system operates in a normal mannersuch that expanding refrigerant in the evaporator removes heat from theseries of ice forming sites, freezing the water to form an outwardlygrowing layer of ice. When the ice thickness reaches a predeterminedcondition or a specified time period has elapsed, the ice making machineswitches to harvest mode.

Typically the harvest mode involves a valve change which directs hotrefrigerant gasses to the evaporator. The ice forming locations areheated by the hot refrigerant gasses until the ice in contact with theevaporator begins to thaw. Once the ice falls from the evaporator, it iscollected by an appropriate ice bin. When more ice is required, therefrigerant system is switched back to the production mode and the cyclebegins again. These cycles continue until there is sufficient ice in theice bin.

SUMMARY

In accordance with one aspect of the invention, an evaporator comprisesa refrigerant conduit and front and rear plates sandwiching therefrigerant conduit. The front and rear plates have inner flat portions,each inner flat portion of the front plate facing, but being spacedfrom, a respective inner flat portion of the rear plate to define arespective spaced portion. The front and rear plates also include a setof first protrusions, each first protrusion on the front plate facing arespective first protrusion on the rear plate to define a respectiveactive cavity. The refrigerant conduit extends through each of theactive cavities. The front and rear plates further include a set ofsecond protrusions, each second protrusion on the front plate facing arespective second protrusion on the rear plate to define a respectivepassive cavity. The refrigerant conduit does not extend through any ofthe passive cavities. The location of the active and passive cavitiesare interspersed and separated by respective inner flat portions so asto define a plurality of ice forming sites.

In a preferred embodiment, the evaporator uses a single refrigerantconduit having a serpentine shape. However, a plurality of refrigerantconduits can be used. For example, a first refrigerant conduit can beused for the upper half of the evaporator and a second refrigerantconduit can be used for the lower half of the evaporator. In eithercase, a portion of at least one of the refrigerant conduits preferablyextends through each of the active cavities.

The refrigerant conduit is preferably a pipe having grooves formed alongits inner surface so as to increase the inner surface area of the pipeand thereby improve the heat transfer between the refrigerant flowingthrough the pipe and the ice forming surfaces of the protrusionsdefining the ice forming cavities. The inner groves preferably runhelically along the inner surface of the pipe.

Each active cavity is preferably surrounded by a pair of inactivecavities which are connected to the active cavity by respective spacedportions. The spacing between the inner flat faces defining therespective spaced portions, as measured along a line runningperpendicular to the flat faces is preferably between 1 and 2 mm. Thisis important because if the flat portions abut one another it has beenfound that corrosion can occur.

It has also been found that spaces between the inner walls of the activecavities and the refrigerant conduit passing through them can lead tocorrosion of the protrusions forming the active cavities. This can leadto holes being formed in the protrusions which can allow water to enterthe active cavities. If that happens water can freeze and melt duringthe ice making and ice harvesting cycles and can deform the plate and/orthe refrigerant conduit. This decreases the heat transfer between therefrigerant in the refrigerant conduit and the outer surfaces of theactive cavities and eventually can block refrigerant from passingthrough the refrigerant conduit. In order to avoid this problem, it ispreferred that the outer surfaces of the refrigerant conduit are pressedagainst (abut) the inner surfaces of the protrusions except for the areawhere the spaced portions meet the active cavity.

In the preferred embodiment, each protrusion of the respective pair hasan outer flat portion surrounded by a pair of curved portions extendingfrom the outer flat portion to the respective pair of inner flatportions. The refrigerant conduit takes the same form.

In one embodiment, the front and rear plates are connected to oneanother by an appropriate fastener such as bolts or rivets which extendthrough elongated slots in the front and rear plates. Because the slotsare elongated, and preferably formed at a 45 degree angle with respectto the plane in which the inner flat portions lie, the slots need not beperfectly located in order to ensure that they will overlap allowing foreasier assembly of the evaporator.

Each of the front plate and the rear plate preferably includes aplurality of fins, which divide each of the front plate and the rearplate into a plurality of ice forming columns each including a pluralityof ice forming sites. The ice forming columns preferably run parallel toone another and perpendicular to the direction that the at least onerefrigerant conduit passes through the active cavities.

In another aspect of the invention, an ice making system comprises arefrigerant system for circulating cold refrigerant through anevaporator and a source of water applying liquid water to the evaporatorto form ice on the evaporator. The evaporator includes a refrigerantconduit and front and rear plates sandwiching the refrigerant conduit.The front and rear plates have inner flat portions, each inner flatportion of the front plate facing, but being spaced from, a respectiveinner flat portion of the rear plate to define a respective spacedportion. The front and rear plates also include a set of firstprotrusions. Each first protrusion on the front plate faces a respectivefirst protrusion on the rear plate to define a respective active cavity.The refrigerant conduit extends through each of the active cavities. Thefront and rear plates further include a set of second protrusions. Eachsecond protrusion on the front plate faces a respective secondprotrusion on the rear plate to define a respective passive cavity. Therefrigerant conduit does not extend through any of the passive cavities.The locations of the active and passive cavities are interspersed andseparated by respective inner flat portions so as to define a pluralityof ice forming sites. The source of water applies liquid water to thefirst and second plates whereby ice is formed at the ice forming sites.

The source of refrigerant can switch between a cooling cycle, in whichcooling refrigerant is passed through the refrigerant conduit(s) and iceis formed, and a harvesting cycle, wherein a warming refrigerant ispassed through the refrigerant conduit(s) and ice falls off of the iceforming sites and is harvested.

In at least one other aspect of the invention, the front plate or therear plate or the front plate and the rear plate are formed, in part, bybending a flat plate to include the plurality of fins which divide theplate into a plurality of fins to divide them into a plurality of iceforming columns. Each ice forming column preferably includes a pluralityof ice forming sites. To assist in this process, notches are formed onthe top and/or bottom edges of the flat plate at locations correspondingto the locations of the fins. The fins are then formed by bending theflat plates in a preferably triangular shape while using the notches todetermine where to form the fins.

In another aspect, disclosed is an evaporator comprising: a refrigerantconduit; and front and rear plates sandwiching the refrigerant conduit,each of the front and rear plates comprising: a plurality of ice formingcolumns; a set of first protrusions defined in the respective iceforming columns, each first protrusion on the front plate facing arespective first protrusion on the rear plate to define a respectiveactive cavity, the refrigerant conduit extending through each of theactive cavities; a set of second protrusions defined in the respectiveice forming columns, each second protrusion on the front plate facing arespective second protrusion on the rear plate to define a respectivepassive cavity, the refrigerant conduit not extending through any of thepassive cavities; and inner flat portions, each inner flat portion ofthe front plate facing and spaced from a respective inner flat portionof the rear plate to define a respective spaced portion; wherein theactive cavities and passive cavities are interspersed and separated byrespective inner flat portions so as to define a plurality of iceforming sites in the ice forming columns of the respective plate.

In a further aspect, disclosed is an ice making system comprising: arefrigerant system for circulating refrigerant through an evaporator,the evaporator comprising: a refrigerant conduit; and front and rearplates sandwiching the refrigerant conduit, the front and rear platescomprising: a plurality of ice forming columns; a set of firstprotrusions defined in the respective ice forming columns, each firstprotrusion on the front plate facing a respective first protrusion onthe rear plate to define a respective active cavity, the refrigerantconduit extending through each of the active cavities; a set of secondprotrusions defined in the respective ice forming columns, each secondprotrusion on the front plate facing a respective second protrusion onthe rear plate to define a respective passive cavity, the refrigerantconduit not extending through any of the passive cavities; and innerflat portions, each inner flat portion of the front plate facing andspaced from a respective inner flat portion of the rear plate to definea respective spaced portion; wherein the location of the active andpassive cavities is interspersed and separated by respective inner flatportions so as to define a plurality of ice forming sites in the iceforming columns of the respective plate; and a source of waterpositioned above the front and rear plates, the evaporator configured toform ice at each of the respective ice forming sites using liquid waterfrom the source of water.

In yet another aspect, disclosed is a method of manufacturing anevaporator, the method comprising: forming front and rear plates of theevaporator from respective flat plates, each of the front and rearplates further comprising: a plurality of ice forming columns; a set offirst protrusions defined in the respective ice forming columns; a setof second protrusions defined in the respective ice forming columns; andinner flat portions; sandwiching a refrigerant conduit of the evaporatorbetween the front and rear plates, the refrigerant conduit extendingthrough each of the active cavities but not extending through any of thepassive cavities, each first protrusion on the front plate facing arespective first protrusion on the rear plate to define a respectiveactive cavity and each second protrusion on the front plate facing arespective second protrusion on the rear plate to define a respectivepassive cavity, the active and passive cavities being interspersed andseparated by the respective inner flat portions so as to define aplurality of ice forming sites in the ice forming columns of therespective plate; and spacing each inner flat portion of the front platefrom a respective inner flat portion of the rear plate to define arespective spaced portion, each inner flat portion of the front platefacing a respective inner flat portion of the rear plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an evaporator constructed in accordancewith the principles of the present invention.

FIG. 2 is a cross sectional view of portion of the evaporator of FIG. 1taken along lines 2-2 of FIG. 1.

FIG. 3 is the same cross sectional view as FIG. 2 but shows theformation of ice cubes on some of the ice forming sites.

FIG. 4A is a cross sectional view of a pipe forming a preferredembodiment of the refrigerant conduit forming part of the evaporator ofFIG. 1.

FIG. 4B is an enlarged view of a portion of the pipe shown in FIG. 4A.

FIGS. 5A and 5B are enlarged views showing a portion of the outermostfins of the front and rear plates of the evaporator of FIG. 1 before andafter the two plates are connected together.

FIG. 6 is a schematic view of an icemaker incorporating the evaporatorof FIG. 1.

FIG. 7A is a plan view of a flat sheet used to construct the front orrear plate of the evaporator of FIG. 1.

FIG. 7B is a plan view of the flat sheet of FIG. 7A wherein notches havebeen added to the sheet to assist in the accurate formation of fins inthe flat sheet.

FIG. 7C is an isometric view showing fins of the front and rear platesof the evaporator of FIG. 1 when the plates are formed using the notchesof FIG. 7B.

FIGS. 8A through 8H show alternative shapes for the notches of FIG. 7B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like numerals indicate likeelements, there is shown in FIG. 1 an evaporator 10 comprising aserpentine refrigerant conduit 12 sandwiched by front and rear plates 14and 16. The refrigerant conduit can be considered a coolant conduit. Thefront and rear plates 14, 16 are preferably divided into a plurality ofvertically extending ice forming columns 18 by a plurality of fins 20. Aplurality of depressions 22, which can be considered dimples, are formedin the ice forming columns 18. In a preferred embodiment, the front andrear plates 14, 16 are formed from respective flat metal sheets. Thesheets are first bent at spaced locations to form the fins 20.Thereafter depressions 22 are formed in the front and rear plates 14, 16using tools similar to those shown in U.S. application Ser. No.14/022,887. When these tools are used, the portion of the refrigerantconduit 12 located adjacent to the depressions 22 is similarly deformed.However, as will become clearer below, the shape of the depressions 22in the present embodiment is different than the shape of the depressionsin U.S. application Ser. No. 14/022,887 in order to achieve variousimprovements in the structure of the evaporator.

As best shown in FIGS. 2 and 3, the depressions 22 are formed in thefront and rear plates to form active cavities 24 and passive cavities26. The refrigerant conduit 12 passes through the active cavities 24 butnot through the passive cavities 26. As a result, the active cavities 24are cooled by the refrigerant passing through the refrigerant conduit 12during the ice forming cycle and, when water is applied to the surfacesof the front and rear plates 14, 16, will form ice cubes on ice formingsites 28 described in further detail below.

The depressions 22 have an inner flat portion 30 surrounded by twocurved portions 32 which terminate at an outer flat portion 34 locatedbetween adjacent depressions. In the preferred embodiment, the innerflat portions 30 lie in a first plane and the outer flat portions 34 liein a second plane, parallel to and spaced from the first plane. Eachinner flat portion 30 on front plate 14 opposes a corresponding innerflat portion 30 on the rear plate 16 but is spaced from the opposedinner flat portion.

The combination of the curved portions 32 and the outer flat portions 34on the front plate 14 define a series of first and second protrusions36, 38 on the front plate 14, and the combination of the curved portions32 and the outer flat portions 34 on the rear plate 16 similarly definea series of first and second protrusions 36, 38 on the rear plate 16.Each first protrusion 36 on the front plate 14 opposes a correspondingfirst protrusion on the rear plate 16 to form a respective active cavity24. Each second protrusion 38 and the front plate 14 opposes acorresponding second protrusion on the rear plate 16 to form arespective passive cavity 26. Respective pairs of inner flat portions 30face one another to form respective spaced portions 40. As noted above,it has been found that if the inner flat portions 30 abut one anothercorrosion can occur. To avoid this problem, the opposed inner flatportions are spaced apart, preferably by 1-2 mm.

Each first protrusion 36 (forming part of a respective active cavity 24)is located between an adjacent pair of second protrusions 38 (formingpart of respective passive cavities 26) and is connected thereto byrespective spaced portions 40.

A portion of the refrigerant conduit 12 passes through and is in thermalcontact (and more preferably in direct physical contact) with the firstand second protrusions 36, 38 forming each of the active cavities 40. Asa result, there is an efficient transfer of heat from the refrigerant inthe refrigerant conduit 12 to the outer surface of the first protrusions36. This will define the heart of the ice forming site 28—ice will formon the first protrusion 36 and will grow laterally outwardly, preferablyonto its adjacent inner flat portions 30 and onto at least part of thecurved portions 32 of the adjacent second protrusions 38 forming part ofthe adjacent passive cavities 26.

This is best seen in FIG. 3, which shows the formation of ice cubes 42on the rear plate 16. Similar ice cubes, not shown, will be formed onthe ice forming sites 28 of the front plate 14. The degree to which theice extends over the inner flat portions 30 and the adjacent secondprotrusions 38 is determined, at least in part, by the length of timethat water is applied to the front and rear plates 14, 16 during the iceforming cycle.

Once ice cubes 42 of sufficient size have been formed, the system willswitch to a harvesting cycle wherein relatively warm coolant is passedthrough the refrigerant conduit 12 and the ice cubes 42 will separatefrom the ice forming sites 28 and be collected in an ice bin 60discussed further below.

In the preferred embodiment, a single refrigerant conduit 12 having aserpentine shape is used. It includes a plurality of straight portionswhich run perpendicular to the ice forming columns 18 and curvedportions located outside of the front and rear plates 14, 16 andconnecting the straight portions. While a single refrigerant conduit 12is preferred, more than one conduit can be used. By way of example andnot limitation, a first cooling conduit can be used for the upper halfof the evaporator 10 and a second cooling conduit can be used for thelower half of the evaporator 10.

The refrigerant conduit 12 is preferably a round pipe. However, duringassembly of the evaporator 10, the pipe is placed between the front andrear plates 14, 16 and dies or other means are used to form thedepressions 22 (and therefore the active and passive cavities 24, 26)thereby deforming portions of the pipe extending between the front andrear plates 14, 16 into the generally ovoid shape shown in FIGS. 2 and3. As a result, the outer surface of the pipe and the inner surface ofthe active cavities 40 are pressed against one another. This ensuresgood thermal conduction between the refrigerant passing through therefrigerant conduit 12 and the outer surfaces of the first protrusions36. In the preferred embodiment, the outer surface of the refrigerantconduit 12 directly abuts the inner surface of the first protrusions 36.However, it is possible to provide another material interfacing thosesurfaces as long as the material has a sufficiently high thermalconductivity to ensure efficient transfer of energy between the outersurface of the first protrusion 36 and the coolant passing through therefrigerant conduit 12.

To further improve the thermal conductivity between the refrigerant andthe outer surfaces of the first protrusion 36, grooves 44 (see FIGS. 4Aand 4B) are preferably formed on the inner surface of the refrigerantconduit 12 to increase its inner surface area. The grooves preferablyrun in a helical manner relative to an axial center of the refrigerantconduit 12. The grooves 44 define projections 46 having the shape shownin FIG. 4B. More particularly, they are wider at their proximal basethan at their distal tip and the tips are preferably rounded.

As best shown in FIGS. 1, 5A, and 5B, projections 48 are formed on theoutermost fins 50 and elongated slots 52 are formed in the projections48 to receive rivets, bolts, or other connection means (not shown) tohold the front and rear plates 14, 16 together. The elongated slots arepreferably formed at a 45 degree angle relative to the plane of theinner flat portions 30 and at 90 degrees with respect to one another.

In the past, round rivet receiving holes had been formed in theprojections 48. However, this often made it difficult to pass the rivetthrough the holes due to tolerance errors or other variations in theprocess of forming the evaporator 10. The use of these elongated slots52, especially when they run at a 45 degree angle relative to the planeof the inner flat portions 30 and at 90 degrees with respect to oneanother, overcomes this problem.

An ice forming machine 54 incorporating the evaporator 10 of the presentinvention is shown schematically in FIG. 6. The ice forming machine 54includes a refrigerant system 56, a water supply 58, and an ice bin 60.The evaporator 10 forms part of the refrigerant system 56 which alsoincludes a compressor 62, a condenser 64, and an expansion valve 66. Therefrigerant system 56 preferably includes a valve 68, which switchesbetween a first position where it passes low-temperature, low-pressureliquid refrigerant exiting the expansion valve 66 to the refrigerantconduit 12 of the evaporator 10 and a second position where it passeshigh-temperature, high-pressure gas existing the compressor 62 to therefrigerant conduit 12. A controller (not shown) detects how much ice isin the ice bin 60 and moves the refrigeration system between iceproduction and ice harvesting modes as a function thereof. When thecontroller determines that there is insufficient ice in the ice bin 60,it moves valve 68 into its first position so that low-temperature,low-pressure liquid coolant is supplied to the refrigerant conduit 12thereby initiating the ice production mode. The controller maintains thevalve 60 in this position until sufficiently sized ice cubes 42 areformed on the ice forming sites 28 and then switches the valve 68 intothe second mode so that high-temperature, high-pressure coolant gas issupplied to refrigerant conduit 12 to thereby begin operation in the iceharvesting mode. During this mode, the temperature of the surface of theice forming sites 28 will be raised and the ice cubes 42 will eventuallyseparate from the ice forming sites 28 and be collected in the ice bin60. If, after the harvesting mode has ended, there is still insufficientice in the ice bin 60, the controller will recycle the refrigerantsystem 56 through the ice forming and ice harvesting modes until thereis a sufficient level of ice in the ice bin 60. Once a sufficient amountof ice is in the ice bin 60, the controller will typically shut down therefrigerant system 56 until additional ice is required.

A process for forming the fins 20 in the front and rear plates 14, 16will now be described with reference to FIGS. 7A, 7B and 7C. As shown inFIGS. 7A and 7B, each front and rear plate starts out as a rectangular,typically metal, plate. The fins 20 have to be formed at preferablyequally spaced locations along the plate (only one such location isshown in FIG. 7A). Each fin 20 is formed by a bending machine (notshown) which bends the plate along three lines 70, 72, and 74 to formthe triangular fin 20 shown in FIG. 7C.

After a given fin 20 is formed, a plate roller machine (not shown) movesthe plate by a distance corresponding to the desired distance betweenadjacent fins 20. However, due to slippage and other variables, forexample if the feeding direction is not perpendicular to the location ofthe bending machine, it is difficult to accurately and reliably do so.In order to overcome this problem, the present aspect of the inventionadds notches 76 to at least one of the side surfaces of the plate. Thespacing of the notches 76 corresponds to the desired spacing of the fins20. In the preferred embodiment, the notches 76 are located at thecenter line 72 corresponding to the center of the fins 20. However, thenotches 76 need not be located at this position as long as they have aspacing that allows the plate roller machine to accurately locate thecenter line 72 of the fins 20. A locator 78 is then used to locate theposition of the notch 76 and a controller (not shown) uses thisinformation to cause the plate roller machine to accurately position thesheet relative to the bending machine, thereby ensuring that the fins 60are formed at the correct locations.

Because of the use of the notches 76, the top and/or bottom of the frontand rear plates 14, 16 will include a chamfer as shown in FIG. 7A. Inthe preferred embodiment, the notch 76 is a triangular notch and thechamfer has the shape shown. However, the notches can take other shapes(e.g., round, square, etc.) resulting in different chamfer profiles (asprojected along a plane running perpendicular to the plane of the innerflat portions 30) such as those shown in FIGS. 8A-8H.

While the invention has been described in conjunction with regards tospecific aspects, it is evident that various changes and modificationsmay be made, and the equivalents substituted for elements thereofwithout departing from the true scope of the invention. In addition,many modifications may be made to adapt a particular situation ormaterial to the teachings of the invention without departing from thescope thereof. Therefore, it is intended that this invention not belimited to the particular aspects disclosed herein, but will include allembodiments within the spirit and scope of the disclosure.

That which is claimed is:
 1. An evaporator comprising: a refrigerantconduit; and front and rear plates sandwiching the refrigerant conduit,each of the front and rear plates comprising: a plurality of ice formingcolumns; a set of first protrusions defined in the respective iceforming columns, each first protrusion on the front plate facing arespective first protrusion on the rear plate to define a respectiveactive cavity, the refrigerant conduit extending through each of theactive cavities; a set of second protrusions defined in the respectiveice forming columns, each second protrusion on the front plate facing arespective second protrusion on the rear plate to define a respectivepassive cavity, the refrigerant conduit not extending through any of thepassive cavities; and inner flat portions, each inner flat portion ofthe front plate facing and spaced from a respective inner flat portionof the rear plate to define a respective spaced portion; wherein theactive cavities and passive cavities are interspersed and separated byrespective inner flat portions so as to define a plurality of iceforming sites in the ice forming columns of the respective plate.
 2. Theevaporator of claim 1, wherein the refrigerant conduit has a serpentineshape.
 3. The evaporator of claim 1, wherein the spacing between eachrespective pairs of inner flat faces defining the respective spacedportion is between 1 and 2 mm as measured along a line runningperpendicular to the inner flat faces.
 4. The evaporator of claim 1,wherein each of the first protrusions defining a respective activecavity defines a pair of curved portions, a surface of each of the pairof curved portions in thermal contact with an outer surface of therefrigerant conduit extending through the respective active cavity. 5.The evaporator of claim 1, wherein the front and rear plates areconnected to one another by fasteners extending through elongated slotsin the front and rear plates.
 6. The evaporator of claim 1, wherein theelongated slots are formed in outermost fins of the front and rearplates.
 7. The evaporator of claim 1, wherein each of the ice formingcolumns extends in a vertical direction.
 8. The evaporator of claim 1,further comprising a plurality of fins dividing each of the respectivefront and rear plates into the ice forming columns.
 9. The evaporator ofclaim 8, wherein each of the plurality of fins is formed by bending aone of the respective front and rear plates into a triangular shape incross-section.
 10. The evaporator of claim 8, wherein each of theplurality of fins has upper and lower ends that, when projected onto aplane running perpendicular to the inner flat portions, defines a notch.11. An ice making system comprising: a refrigerant system forcirculating refrigerant through an evaporator, the evaporatorcomprising: a refrigerant conduit; and front and rear plates sandwichingthe refrigerant conduit, the front and rear plates comprising: aplurality of ice forming columns; a set of first protrusions defined inthe respective ice forming columns, each first protrusion on the frontplate facing a respective first protrusion on the rear plate to define arespective active cavity, the refrigerant conduit extending through eachof the active cavities; a set of second protrusions defined in therespective ice forming columns, each second protrusion on the frontplate facing a respective second protrusion on the rear plate to definea respective passive cavity, the refrigerant conduit not extendingthrough any of the passive cavities; and inner flat portions, each innerflat portion of the front plate facing and spaced from a respectiveinner flat portion of the rear plate to define a respective spacedportion; wherein the location of the active and passive cavities isinterspersed and separated by respective inner flat portions so as todefine a plurality of ice forming sites in the ice forming columns ofthe respective plate; and a source of water positioned above the frontand rear plates, the evaporator configured to form ice at each of therespective ice forming sites using liquid water from the source ofwater.
 12. The system of claim 11, further comprising a plurality offins dividing each of the respective front and rear plates into the iceforming columns.
 13. The system of claim 12, wherein each of theplurality of fins is formed by bending a one of the respective front andrear plates into a triangular shape in cross-section.
 14. The system ofclaim 11, wherein each of the ice forming columns extends vertically,the source of water configured to apply liquid water to each of therespective ice forming columns.
 15. The system of claim 11, wherein eachof the first protrusions defining a respective active cavity defines apair of curved portions, a surface of each of the pair of curvedportions in thermal contact with an outer surface of the refrigerantconduit extending through the respective active cavity.
 16. A method ofmanufacturing an evaporator, the method comprising: forming front andrear plates of the evaporator from respective flat plates, each of thefront and rear plates further comprising: a plurality of ice formingcolumns; a set of first protrusions defined in the respective iceforming columns; a set of second protrusions defined in the respectiveice forming columns; and inner flat portions; sandwiching a refrigerantconduit of the evaporator between the front and rear plates, therefrigerant conduit extending through each of the active cavities butnot extending through any of the passive cavities, each first protrusionon the front plate facing a respective first protrusion on the rearplate to define a respective active cavity and each second protrusion onthe front plate facing a respective second protrusion on the rear plateto define a respective passive cavity, the active and passive cavitiesbeing interspersed and separated by the respective inner flat portionsso as to define a plurality of ice forming sites in the ice formingcolumns of the respective plate; and spacing each inner flat portion ofthe front plate from a respective inner flat portion of the rear plateto define a respective spaced portion, each inner flat portion of thefront plate facing a respective inner flat portion of the rear plate.17. The method of claim 16, further comprising forming a plurality offins in each of the front and rear plates by bending the respectiveplates into a triangular shape in cross-section at each of the pluralityof fins, each of the plurality of fins forming the respective ice makingcolumns.
 18. The method of claim 16, further comprising: formingelongated slots in outermost fins of the front and rear plates; andconnecting the front and rear plates to one another by fastenersextending through the elongated slots.
 19. The method of claim 16,wherein forming the front and rear plates of the evaporator comprisesforming pairs of curved portions in each of the set of first protrusionsand the set of second protrusions, a surface of each of the pairs ofcurved portions in thermal contact with an outer surface of therefrigerant conduit extending through the respective active cavity. 20.The method of claim 16, wherein forming the front and rear plates of theevaporator occurs while sandwiching the refrigerant conduit of theevaporator between the front and rear plates.